Virtually all RF transmitters with quadrature topologies (e.g. not polar, EER, etc.) contain various non-idealities. These non-idealities may include imbalances between the quadrature branches (e.g., I/Q (or, alternatively, IQ) imbalances between the I and Q branches of the I/Q modulator). These I/Q imbalances mainly depend on the transmitter circuit design and manufacturing process variations, and may distort transmitted signals and degrade the quality of the transmitter. Moreover, once the device implementing the transmitter is in the “field,” (i.e., during ordinary use), these imbalances will further vary over time. Thus, these I/Q imbalance variations depend in the short-term on the supply voltage variations, silicon temperature variations, operating frequency, etc., and in the long term on silicon aging. Therefore, compensating for I/Q imbalances is an arduous task.
Non-idealities may also include non-linear characteristics of one or more amplifier stages implemented as part of the transmitter design. For instance, it is common for transmit analog/RF front-ends (TX-AFE) with low power consumption constraints to present nonlinear behavior, or be designed to operate in nonlinear regions (e.g. to optimize power efficiency). The nonlinear behavior can become even more complex when RF memory effects come into play (generating so-called AM-PM, PM-PM and PM-AM type distortions). And, like the I/Q imbalances, TX-AFE nonlinearities are also subject to variations throughout time (e.g. depending in the short-term on temperature, supply voltage, and operating frequency variations, and on the long-term on silicon aging). Therefore, compensating for such nonlinearities is likewise a complex task.
The exemplary aspects of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.